This invention relates generally to so-called active-suspension systems of vehicles, particularly motor vehicles, and more particularly to a system for controlling such suspension systems.
In a motor vehicle in which an air-suspension system is used, the air pressure in each air-suspension unit of the system is regulated by an air regulating system which ordinarily comprises a flow control valve having a charging-side valve and a discharging-side valve, a high-pressure tank connected to the charging-side valve, a low-pressure tank connected to the discharging-side valve, and an air compressor connected on its suction side to the low-pressure tank and on its delivery side to the high-pressure tank, and outlet and inlet ports respectively of the charging-side and discharging-side valves being connected to an air suspension unit. Ordinarily one air suspension unit is provided for each independent wheel of the vehicle.
In the following disclosure, descriptions are set forth with respect to a single suspension unit, for the most part, but it is to be understood that the descriptions are applicable to all suspension units.
The air compressor operates to draw air from the low-pressure tank, to compress this air, and to deliver the compressed air to the high-pressure tank. When the charging-side valve is opened, air at high pressure is supplied to the air-suspension unit, and, when the discharge-side valve is opened, the air in the air-suspension unit is discharged into the low-pressure tank. The air regulating system briefly described above is a so-called closed pneumatic circuit system which is known in the art, one disclosure thereof being set forth in Japanese Patent Publication No. 50-28589.
When a closed pneumatic circuit system as described above is provided in combination with a group of sensors for detecting the various motions of the air suspension units and a controller for controlling the opening and closing actions of the flow control valves in response to signals from the sensors, the air regulating system is an active suspension system capable of variably controlling the damping, spring action, and other characteristics of the air suspension units and also the attitude of the vehicle. An example of such a system will be described more fully hereinafter.
In an active suspension system as described above, a difference to some extent inevitably occurs between the desired flow quantity transmitted by the above-mentioned controller and the actual flow quantity of the air charged or discharged through each flow control valve, because of various causes such as dynamic time delay or delay in the riser portion of the valve characteristic at the time of valve operation. Accordingly, it is necessary to carry out compensatory correction for this difference.
One method of compensatorily correcting this difference which would appear to be possible is to measure the actual flow quantity by means of a flow quantity sensor such as a flow quantity meter and to feed back the difference between this measured actual flow quantity and the control desired flow quantity thereby to accomplish correction of the control desired flow quantity. This method, however, requires precise hardware such as flow quantity meters and the provision of feedback circuits. As a consequence, not only does the system become expensive, but the circuitry also becomes complicated, whereby it is considerably difficult to reduce this method to practice.